JP2679825B2 - Ignition timing control device for two-stroke engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an ignition timing control device that retards an ignition timing in a high speed rotation range equal to or higher than a maximum torque generating rotation speed.

[Prior Art] In a two-cycle engine, in order to improve the charging efficiency of fresh air, a negative pressure reflected wave is applied to the exhaust port during the opening period of the scavenging port to accelerate the suction of the exhaust gas and close the scavenging port. From the beginning until the exhaust port is closed, a positive pressure reflected wave is applied to the exhaust port to push the fresh air blown into the exhaust pipe back to the combustion chamber.

In this way, when the filling efficiency of fresh air is enhanced by utilizing the arterial effect of exhaust gas, the timing at which the pressure reflected wave returns to the exhaust port is greatly affected by the pipe length and diameter of the exhaust pipe, etc.
The shape and size of the exhaust pipe are often set in accordance with the maximum torque generation rotational speed range.

However, in an engine, such as a racing engine, which frequently uses a high-speed rotation range equal to or higher than the maximum torque generation speed, the exhaust pipe receives the running wind during high-speed running and is efficiently cooled. Exhaust temperature tended to decrease. Then, the sound velocity of the exhaust gas in the exhaust pipe decreases, and the timing at which the pressure reflected wave returns to the exhaust port tends to be delayed, causing a problem that the output characteristic of the engine sharply decreases.

Therefore, in the past, for example, "Japanese Patent Laid-Open No. 62-70660"
As can be seen from the above, when the engine speed reaches the high-speed rotation range of the maximum torque generation speed or more, the ignition timing is positively retarded to increase the combustion temperature and eventually the exhaust temperature in the exhaust pipe. An ignition timing control device is known in which the timing at which the pressure reflection liquid of the exhaust gas returns to the exhaust port is synchronized.

In this control device, the optimum exhaust temperature at which the maximum torque is obtained with respect to the engine speed is stored as data, and the optimum exhaust temperature for the engine speed is read from the above data during engine operation. The actual exhaust temperature detected by the sensor is compared, and the ignition timing is retarded so that the actual exhaust temperature approaches the optimum exhaust temperature when the engine speed reaches the high speed rotation range.

[Problems to be Solved by the Invention] By the way, when the ignition timing is adjusted by detecting the exhaust gas temperature in the exhaust pipe, in order to adjust the ignition timing appropriately, the sensitivity of the temperature sensor should be increased. It is desired to detect the transition of temperature accurately and sensitively.

However, since the temperature sensor is always exposed to high-temperature and high-pressure exhaust gas, if the temperature sensor is made to react sensitively to the exhaust temperature, the temperature sensor may become too thin and the durability may deteriorate. Therefore, considering the durability, the sensitivity of the temperature sensor cannot be increased so much, and therefore, in the above-described conventional control device, the timing of retarding the ignition timing or conversely advancing the ignition timing may be delayed. It was. Therefore, especially if the ignition timing is retarded, the engine may misfire, so this misfire state may continue due to insufficient sensitivity of the temperature sensor, which adversely affects the output characteristics of the engine. There is.

The present invention has been made based on such a situation, and it is possible to accurately detect the pressure change in the exhaust passage in the high speed rotation range, and to control the retard amount of the ignition timing at an appropriate timing. It is an object of the present invention to provide an ignition timing control device for a two-cycle engine capable of achieving the above.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an exhaust port which is opened in an inner surface of a cylinder and is opened and closed by a piston; An exhaust pipe having a shape that is gradually expanded and its diameter is gradually reduced from the maximum diameter portion toward the exhaust downstream side;
An ignition timing control device applied to a two-cycle engine having an exhaust passage including a control unit, and retards the ignition timing when the engine speed reaches a high-speed rotation range of a maximum torque generation rotation speed or more. It is assumed.

The ignition timing control device is disposed at the upstream end of the exhaust passage, and has means for detecting the pressure of the exhaust gas discharged into the exhaust passage; and the actual pressure value detected by this means and the preset value. When the engine speed is in the high-speed rotation range above the maximum torque generation speed and the actual pressure in the exhaust passage exceeds the reference value, the ignition timing is retarded by comparing with the reference value of pressure. It is characterized by including a correction means for reducing the amount.

[Operation] In such a configuration, when a misfire occurs in the high speed rotation range where the ignition timing is now retarded, unburned raw gas is discharged to the exhaust passage. In this case, the inside of the exhaust passage is
Since a high temperature and high pressure atmosphere is created due to the ignition timing retard control, if a large amount of raw gas is discharged into this atmosphere, combustion of the air-fuel mixture starts in the exhaust passage and the pressure in the exhaust passage rises. . Then, since there is a means for detecting the pressure at the upstream end of the exhaust passage, the pressure increase in the exhaust passage is directly detected with high accuracy, and the correction means is used to immediately reduce the retard amount of the ignition timing. It for that reason,
In a high-speed rotation range equal to or higher than the maximum torque generation rotation speed, the misfire state does not continue unlike the conventional case, and the retard amount of the ignition timing can be controlled at an appropriate timing.

[Example] The present invention will be described below based on an example shown in the drawings.

In FIG. 1, reference numeral 1 is a two-cycle engine for a motorcycle, 2 is its cylinder, 3 is a combustion chamber, and 2 is a cylinder.
An intake port 5, a scavenging port 6, and an exhaust port 7 which are opened and closed by a piston 4 are opened on the inner surface of the. An exhaust pipe 8 is connected to the exhaust port 7, and the diameter of the exhaust pipe 8 is gradually increased as it goes to the exhaust downstream side, and the diameter is gradually decreased as it goes from the maximum diameter portion to the exhaust downstream side. The expansion chamber 9 having such a shape is provided. The exhaust pipe 8 and the exhaust port 7 form an exhaust passage 18 of the two-cycle engine 1.

By the way, in the case of the present embodiment, at the upstream end of the exhaust pipe 8 on the exhaust port 7 side, a pressure sensor as means for detecting the pressure of the exhaust gas actually discharged from the exhaust port 7 during engine operation.
Ten are provided. The pressure signal output from the pressure sensor 10 is input to the control circuit 12 via the amplifier 11. In the control circuit 12, when the engine speed reaches the high-speed rotation range that exceeds the maximum torque generation speed, the pressure sensor
The actual pressure in the exhaust pipe 8 detected in 10 is compared with a preset reference value of the pressure, that is, a value indicating the pressure in the exhaust pipe 8 when the engine 1 misfires.

Further, a rotation speed signal from a circuit number detector 13 that detects an actual engine rotation speed is input to the control circuit 12 through an amplifier 14. The control circuit 12 stores in advance the ignition timing at which the maximum torque is obtained with respect to the rotation speed of the engine 1 as data, and the control circuit 12 determines the optimum ignition timing based on the signal from the rotation speed detector 12. At the same time as reading, this ignition timing signal is output to the ignition device 15. In addition,
Reference numeral 16 in FIG. 1 is an ignition plug.

 Next, the operation of the above configuration will be described.

When the engine 1 is now started and is in the operating state, the pressure signal from the pressure sensor 10 and the signal from the rotation speed detector 13 are input to the control circuit 12 after being amplified by the amplifiers 11 and 14. Since the control circuit 12 stores the optimum ignition timing for the engine speed as data, the optimum ignition timing for the input speed is read from the data, and this ignition timing control signal is sent to the ignition device 15. Output.

That is, as shown in FIG. 2, the control circuit 12 advances slowly at low speed rotation and then advances the ignition timing with a constant inclination, and when the engine speed reaches the high speed rotation range exceeding the maximum torque generation rotation speed N. , On the contrary, retard the ignition timing. When the ignition timing is retarded in this way, the flame kernel in the combustion chamber 3 is generated later than the predetermined timing, so that the combustion period is after the piston 4 reaches the top dead center.
The burning period becomes longer.

As a result, when the exhaust port 7 is opened, the temperature of the exhaust gas discharged from the exhaust port 7 becomes high and the sonic velocity of the exhaust gas increases, so that the pressure reflected wave of the exhaust gas is substantially the same as that at the maximum torque generation rotational speed. Attempts to return to the exhaust port 7 at the same timing. As a result, the charging efficiency of fresh air can be increased, and the drop in torque in the high-speed rotation range above the maximum torque generation rotation speed is reduced.

On the other hand, since a pressure signal indicating the exhaust pressure in the exhaust pipe 8 is also input to the control circuit 12 via the pressure sensor 10 during engine operation, the control circuit 12 determines that the engine rotation speed is the maximum torque generation rotation speed. When the high speed rotation range is exceeded, this pressure signal is compared with a reference value indicating the pressure in the exhaust pipe 8 when the engine 1 misfires.

That is, as shown in FIG. 3, when the exhaust port 7 is opened, the pressure P in the exhaust pipe 8 rises sharply. According to an experiment conducted by the present inventor, for example, in the case of an 80cc class engine, The pressure P in the exhaust pipe 8 when the ignition timing is retarded in the high-speed rotation range is around 1.5 Kgf / cm ² at the maximum, whereas when the engine 1 misfires in the retarded state, the exhaust pipe 8 It was confirmed that the internal pressure P rapidly increased to about 2.0 Kgf / cm ² . Therefore, if the reference value preset in the control circuit 12 is set to the pressure in the exhaust pipe 8 at the time of misfire, the control circuit 12 will set the reference value of this pressure as shown in FIG. The value is compared with the actual pressure in the exhaust pipe 8, and when the pressure in the exhaust pipe 8 exceeds the reference value,
As indicated by the broken line in FIG. 2, the ignition timing is corrected so that the retard amount in the high speed rotation range decreases.

When the pressure in the exhaust pipe 8 suddenly rises due to the misfire, the pressure sensor 10 immediately detects this and controls the retard amount of the ignition timing at an appropriate timing.
After that, misfire does not occur thereafter, and the output characteristics in the high speed rotation range can be favorably maintained.

Although the pressure sensor is attached to the exhaust pipe in the above embodiment, it may be attached directly to the exhaust port in some cases.

[Effect of the Invention] According to the present invention described in detail above, the presence or absence of misfire in the high-speed rotation range is detected based on the pressure increase in the exhaust passage, and therefore, compared with the conventional case of detecting the exhaust temperature. , It is possible to accurately and accurately control the retard amount of the ignition timing. Therefore, the misfire state does not continue in the high speed rotation range, and the output characteristics in the high speed rotation range can be improved.

[Brief description of the drawings]

FIG. 1 shows an embodiment of the present invention, FIG. 1 is a configuration diagram schematically showing an ignition device of a two-cycle engine, and FIG. 2 is a characteristic showing an advance (retard) amount of ignition timing with respect to an engine speed. FIG. 3 and FIG. 3 are characteristic charts showing changes in pressure in the exhaust pipe, and FIG. 4 is a flow chart showing processing contents in the control circuit. 1 ... 2-cycle engine, 2 ... Cylinder, 4 ... Piston, 7 ... Exhaust port, 8 ... Exhaust pipe, 10 ... Pressure detection means (pressure sensor), 12 ... Correction means (control circuit), 19
...... Exhaust passage.

Claims (1)

(57) [Claims] 1. An exhaust port which is opened on the inner surface of a cylinder and which is opened and closed by a piston; is connected to this exhaust port, and its diameter is gradually increased as it progresses toward the exhaust downstream side, and from its maximum diameter portion to the exhaust downstream side. It is applied to a two-cycle engine equipped with an exhaust passage that includes an exhaust pipe whose diameter is gradually reduced as it progresses; and ignition is performed when the engine speed reaches a high-speed rotation range above the maximum torque generation speed. In an ignition timing control device for retarding the timing, means arranged at the upstream end of the exhaust passage for detecting the pressure of the exhaust gas discharged into the exhaust passage; actual pressure detected by this means Value is compared with a preset pressure reference value, and the engine speed is in the high-speed rotation range of the maximum torque generation speed or more, and the actual pressure in the exhaust passage is the reference value. An ignition timing control device for a two-cycle engine, comprising: a correction unit that reduces the retard amount of the ignition timing when the value exceeds the value.